Mechanics and Actomyosin-Dependent Survival/Chemoresistance of Suspended Tumor Cells in Shear Flow

Tumor cells disseminate to distant organs mainly through blood circulation in which they experience considerable levels of fluid shear stress. However, the effects of hemodynamic shear stress on biophysical properties and functions of circulating tumor cells (CTCs) in suspension are not fully understood. In this study, we found that the majority of suspended breast tumor cells could be eliminated by fluid shear stress, whereas cancer stem cells held survival advantages over conventional cancer cells. Compared to untreated cells, tumor cells surviving shear stress exhibited unique biophysical properties: 1) cell adhesion was significantly retarded, 2) these cells exhibited elongated morphology and enhanced spreading and expressed genes related to epithelial-mesenchymal transition or hybrid phenotype, and 3) surviving tumor cells showed reduced F-actin assembly and stiffness. Importantly, inhibiting actomyosin activity promoted the survival of suspended tumor cells in fluid shear stress, whereas activating actomyosin suppressed cell survival, which might be explained by the up- and downregulation of the antiapoptosis genes. Soft surviving tumor cells held survival advantages in shear flow and higher resistance to chemotherapy. Inhibiting actomyosin activity in untreated cells enhanced chemoresistance, whereas activating actomyosin in surviving tumor cells suppressed this ability. These findings might be associated with the corresponding changes in the genes related to multidrug resistance. In summary, these data demonstrate that hemodynamic shear stress significantly influences biophysical properties and functions of suspended tumor cells. Our study unveils the regulatory roles of actomyosin in the survival and drug resistance of suspended tumor cells in hemodynamic shear flow, which suggest the importance of fluid shear stress and actomyosin activity in tumor metastasis. These findings may reveal a new, to our knowledge, mechanism by which CTCs are able to survive hemodynamic shear stress and chemotherapy and may offer a new potential strategy to target CTCs in shear flow and combat chemoresistance through actomyosin.